1. Field of the Invention
The present invention relates to a starter for starting an engine and, more particularly, to a starter having two-stage rotation speed control.
2. Related Art
The engine compartment of a vehicle is recently packed with more and more engine component parts such as electric accessory equipment. Therefore, reduction in size of a starter is required to meet this over-packed condition. It is proposed, for reducing the size of the starter, to change the moving system of a pinion that engages with the ring gear of the engine.
For instance, in U.S. Pat. No. 5,610,445 (JP-A-7-233770), the pinion that engages with the output shaft of a starter motor through a helical spline is restricted from rotating when the output shaft rotates in response to the rotating force of the starter motor, thus advancing the pinion to the engine ring gear side by the action of the helical spline. This system enables to reduce the weight of object that is to be driven by an electromagnetic switch in comparison with the currently used system in which an electromagnetic switch drives the pinion that is integral with a clutch. That is, the object to be driven is changed from the heavy weight clutch-integral pinion to a light weight pinion rotation restricting member. Thus, the required work power of the electromagnetic switch can be reduced remarkably, thereby reducing the electromagnetic switch to a smaller size and less electric power consuming.
In the starter using the pinion rotation restricting system, however, the whole output of the starter motor produced from the electric power of a power source such as a battery is applied to the pinion. When the pinion engages the ring gear, the pinion collides with the ring gear at high torque and high rotational speed, causing high collision.
It is proposed in U.S. patent application Ser. No. 08/642,942 filed on May 6, 1996 (JP-A-9-217672) to reduce the collision, that will be caused at the time of engagement, by restricting the output of the starter motor until the pinion advances and abuts the side surface of the ring gear. This system has a first power supply circuit that supplies the electric power to the starter motor through an electric resistor and a second power supply circuit that supplies the electric power to the starter motor by short-circuiting the electric resistor. A first switch and a second switch are provided in the first power supply circuit and the second power supply circuit, respectively, and constructed to turn on sequentially in accordance with the distance of movement of the plunger of the electromagnetic switch. That is, until the pinion completely engages with the ring gear; the first switch turns on first in response to the movement of the plunger to supply the starter motor with electric current that is reduced by the electric resistor. Thus, the starter motor rotates at low torque and low rotational speed. Thereafter, when the plunger moves further and turns on the second switch, the electric resistor is short-circuited to supply the starter motor with the required electric current so that the starter motor rotates at high torque and high rotational speed.
In the case of the starter using the pinion rotation restricting system in which two-stage switch structure, however, the pinion rotation restricting member bends with the movement of the plunger before the pinion engages the ring gear when the spring constant of the resilient material for the pinion rotation restricting member is low. That is, it is desired that, while the pinion rotation restricting member is in pinion rotation restriction operation, the plunger linked with the pinion rotation restricting member is restricted from moving thereby to turn on only the first switch. When the pinion rotation restricting member bends, however, it may occur that the plunger will not be restricted from moving and will move to the final position to turn on the second switch undesirably. As a result, the electric resistor will be short-circuited and the full electric power will be supplied to the starter motor, before the pinion advances to the position of engagement with the ring gear. Thus, the starter motor rotates at high torque and high rotational speed, disabling the restriction of high collision impact at the time of engagement between the pinion and the ring gear.